Summary

For the PNW Section's second October 2011 meeting, researchers at Microsoft Research gave details on their proposed system to allow Wi-Fi-like digital data transmissions in the same radio frequency spectrum ("whitespace") that many wireless microphones can use, without causing audible interference.

Ranveer Chandra, a Senior Researcher at Microsoft Research, devised the system, working with George Nychis, a Carnegie Mellon University doctoral student interning at MS, and with Thomas Moscibroda and Ivan Tashev of MSR. Ivan also serves on the AES PNW Section committee. The meeting was held at the Microsoft Research building on the MS campus in Redmond, WA.

Ranveer noted that operating Wi-Fi-style data devices in the RF spectrum vacated by analog television transmissions, but still widely used by wireless microphones, was highly desirable for technical reasons. However, following FCC rules about interference with wireless microphones was not trivial. The traditional Wi-Fi scheme was not suitable in the whitespace situation, and he described a project to test "smart" cognitive transmission methods on the MS shuttle buses' Wi-Fi systems. Encouraged by this, they further knew they had other constraints, such as the FCC rules, the need for complete inaudibility to microphones, the constantly changing spectrum use by mikes, and the desirability of requiring no changes in equipment or behavior on the part of the microphone users.

A testing procedure was described to evaluate methods to make data transmissions inaudible to microphones. Six name-brand microphones were tested under laboratory conditions. They determined that carefully notching and controlling the data transmission power level, thus avoiding a microphone's transmission spectrum, was sufficient, and that the data transmission power within the notch needed to be kept below the microphone's squelch tone level. The full implementation of this technique they call "SEISMIC," for Spectrum Efficient Interference Free System for Microphones." George Nychis would describe this in detail after the break.

A lab demonstration system was on hand to experiment with during the break.

Continuing after the break, George Nychis spoke on how the SEISMIC system would work. Optimally, a detection device they call a "mic protector" would be positioned near wireless microphone receivers, possibly sharing the receiving antennas. The protector would communicate with smart White Space Devices (WSD). Together, they find spectrum in use, ramp up data transmission power, detect when it begins to affect microphone transmissions, and reduce power in appropriate parts of the spectrum. Power levels are constantly evaluated and refined so as to not interfere. Certainly many difficult scenarios can be envisioned, such as hundreds of mikes and/or hundreds of data users, and instances of no "protector" devices being used. The system has been shown to the FCC and microphone manufacturers, and further testing is underway.

An interactive media replay of the presentation will be available to the public on the Microsoft Research website.